The present invention relates to an injection-molding machine having an improved mold support for permitting quick mold removal and installation and a method for quickly removing and installing mold elements. The present invention also relates to an improved drive arrangement for opening and closing the molding machine.
Injection-molding machines generally comprise a stationary platen having a first mold plate, a movable platen having a second mating mold plate, and means for moving the second mold plate toward and away from the first mold plate. U.S. Pat. Nos. 3,174,189 to Cutler et al. and 4,416,064 to Bender et al. exemplify known injection molding machines.
Injection-molding machines are relatively expensive pieces of equipment. Prolonged downtimes to change molds for the production of different items and/or to replace worn or damaged molds are undesirable. Considerable effort has been spent to reduce such downtime by providing molding machines having quick-change mold systems i.e. mold assemblies which can be introduced and removed relatively rapidly. U.S. Pat. No. 4,500,274 to Cyriax et al., for example, shows a quick mold changing method in which a mold is automatically loaded and clamped by means of rollers mounted on the machine platens. U.S. Pat. No. 4,500,275 to Ruhl shows a machine clamping method for quickly clamping the end plates of a mold.
U.S. Pat. No. 4,714,421 to D'Agostino illustrates the use of a "T" slot approach for loading and unloading inserts into mold bases. In this approach, each clamping plate is machined to provide a "T" slot for the extending ears of a T-plate which mates with an interchangeable mold plate.
These quick change approaches unfortunately cannot be applied to stack mold injection molding machines. Such machines are popular because they can be used to increase production. They typically comprise three or more mold plates arranged so as to permit opposing faces of adjacent mold plates to be brought together. U.S. Pat. Nos. 4,154,666 to Ward and 4,408,981 to Brown illustrate known stack mold injection molding machines.
One of the problems faced by all stack mold injection molding machines is proper alignment of the mold plates. For a stack mold to operate properly, the mold plates must have equal spacing between them at all times. Ward and Brown both use a rack and pinion arrangement to maintain proper spacing between the mold plates.
Another problem with stack mold injection molding machines is the provision of adequate support for the center section of the stack mold. In the Brown patent, a support device is attached to the sides of the stack mold center section and slides along the lower tiebars of the molding machine. The support is restrained from lifting off the tiebar by stirrups which run under the lower tiebar. One of the disadvantages associated with this approach is if the tiebar is supported directly on pads mounted on the machine base at regular intervals then the stirrups would foul the pads as the mold opens and closes. A second disadvantage is that the support device is fastened to the mold, including the ends of the racks, and must be removed before the mold can be removed from the machine, since otherwise it would foul the top tiebars. Still further, the support device must be mounted separately after the mold is loaded into the machine. These additional assembly operations are not conducive to quick mold changing.
As previously discussed, the ability to quickly change molds is desirable from the standpoint of reduced downtime and increased productivity. There is currently available a stack mold injection-molding machine produced by Klockner-Windsor having a mounting frame intended to facilitate quick mold changes. There are however several problems with this machine. For example, the tiebars of the machine pass through bushed holes in the frame. This makes the frame an integral part of the machine, not easily removable without pulling the tiebars. The stability of the frame is questionable as its span of support is limited to its thickness and consequent length of the bushings in the frame. This problem is manifested by the frame tipping or rocking as the mold is clamped or more particularly as it is unclamped. The clearance in the short bushings and the large overhanging mass of the mold cavity halves causes the vertical alignment of the mold's center section to vary which in turn causes wear on the mold's sealing surfaces.
The "Windsor" frame has a vertical key on its inner surface which corresponds with a vertical slot on the outer surface of the mold's center section. Vertical positioning of the mold is achieved by accurately controlling the length of the slot in the mold and the height of the key on the frame. Lateral alignment is achieved by spacers attached to the mold sides which fit against the inner surface of the frame. This arrangement has a major problem when it comes to loading and unloading the mold. The key/slot fit is by definition a close tolerance and the mold must therefore be lowered very accurately and in near perfect alignment with the key to prevent cocking or jamming as it is lowered. Similarly when lifting the mold out, this must be done with very accurate vertical alignment, particularly when the mold has almost left the key/slot engagement. Here there is a great tendency for the mold to cock or jam in the key.
Still another disadvantage of the "Windsor" frame is that the drive mechanism reduces the available space for the operator to reach into the mold area. This is due to its mounting above the lower tiebar. This can be a considerable disadvantage when starting up the mold as the operator must reach into each mold cavity to quickly clean the gates.
The present invention is intended to overcome these disadvantages. Accordingly, it is an object of the present invention to provide an injection molding machine having an improved frame for supporting and facilitating the quick removal and installation of mold portions.
It is a further object of the present invention to provide a frame as above having particular utility as a stack mold support.
It is yet a further object of the present invention to provide an improved rack/gear drive arrangement for an injection molding machine.
It is still further object of the present invention to provide an improved method for removing and installing mold portions.
These and other objects and advantages of the present invention will become more apparent from the following description and drawings in which like reference numerals depict like elements.